(1) Field of the Invention
This invention relates to the field of pressure controlled fuel supply systems for internal combustion engines which are operationally controlled by variations in the pressure of fuel supplied to the engine.
(2) Discussion of the Prior Art
Extensive commerical application has been made of fuel systems for internal combustion engines operationally controlled by variations in the pressure of fuel supplied to the engine especially of fuel systems for compression ignition (diesel type) engines such as illustrated in U.S. Pat. Nos. 3,139,875 and 3,385,276. All such systems include a source of fuel under pressure, e.g. a fuel pump, and a mechanism for regulating the fuel pressure supplied to each cylinder. To achieve optimum fuel/air ratios under all operating conditions, highly sophisticated refinements have been made in these basic components to permit a carefully scheduled pressure output as a function of operator demand and engine speed.
One particularly important recent refinement has been the provision of a diaphram controlled operator responsive to intake manifold pressure to modulate fuel flow to the engine during operating conditions in which the intake manifold is below rated pressure. Thus, by carefully controlling the amount of fuel metered into each cylinder of an engine dependent in part upon the air pressure within the engine's intake manifold, it is possible to more accurately control the ratio of fuel to air in the gaseous mixture fed to the engine's cylinders. Such refined control is especially desirable in supercharged engines wherein the fuel air ratio received in each cylinder may otherwise become seriously imbalanced under certain operating conditions such as start-up and acceleration. One such device for achieving this result is illustrated in U.S. Pat. No. 3,945,302 wherein a diaphragm operated valve is disclosed for connection in the fuel line between the engine fuel pump and the engine cylinders. An air pressure line is connected between the intake manifold and one side of the diaphragm which is biased by a spring selected and calibrated to provide modulation of the valve restriction to vary the fuel pressure in response to intake manifold pressure whereby the optimum air/fuel ratio can be maintained over a broad range of operating conditions.
Practical experience with the diaphragm operated valve of U.S. Pat. No. 3,945,302 has shown that this valve is particularly susceptible to fuel leakage around the stem connecting the valve plunger to the diaphragm. While the problem can generally be traced to dirt within the seal area, better filtration to keep the dirt out of the seal area has only been partially successful in eliminating the leakage problem.
In addition to leakage, fuel supply systems of the type disclosed in U.S. Pat. Nos. 3,139,875 and 3,385,276 are also susceptible to improper tampering thereby adversely affecting fuel economy and long term durability. In particular, fuel systems of the type noted are generally provided with a drain line to the fuel tank for returning fuel which is not injected into the engine cylinders or which is bleed from the gear pump section of the fuel pump. Users of engines equipped with such fuel systems have discovered that the engine's short term power output can be increased by clamping the drain line. The effects of such unauthorized modification can be extremely adverse including loss of fuel economy and shortened engine life. Numerous attempts have been made to thwart such intentional drain line blockage with varying degrees of success. For example, U.S. Pat. Nos. 3,741,182 and 4,062,336 disclose anti-tampering fuel control devices for fuel systems for the type disclosed above but these devices have still not presented an ideal solution since added expense and complexity are involved in the application of these inventions to known fuel pressure regulation systems.
In the flow regulating valve art generally, it is known to design a check valve for permiting air flow in one direction but preventing liquid flow in the opposite direction as illustrated in U.S. Pat. No. 2,039,109. It is also know to provide a check valve with an adjustment feature to permit adjustment in the flow rate at which the valve will close as illustrated in U.S. Pat. No. 3,450,206. However, neither of these patents suggests a manner by which the above noted problems peculiar to fuel supply systems for internal conbustion engines could be solved.